Tapered helical compact fluorescent lamp

ABSTRACT

An improved electric discharge lamp, such as a fluorescent lamp, is described in accord with one embodiment of the invention as comprising a tapered cylindrical envelope having a helicallyshaped channel of nonuniform pitch therein for providing a discharge path circumferentially around the envelope with a pair of electrodes disposed adjacent each end of the discharge path. Means are also disclosed for coating the interior surface of the envelope with a luminescent material and filling the envelope with an ionizable gas.

[4 1 Aug. 12, 1975 TAPERED HELICAL COMPACT FLUORESCENT LAMP [75] Inventor: I-Iarald L. Witting, Burnt Hills, NY.

[73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: May I, 1974 [21] Appl. No.: 465,901

[52] US. Cl. 313/493; 313/220; 313/318; 315/59 [51] Int. Cl. H01J 17/34; H01] 61/33 [58] Field of Search 313/220, 493, 204, 317, 313/487, 318; 315/59 [56] References Cited UNITED STATES PATENTS 2,491,847 6/1946 Breadner et a1. 313/317 2,501,375 3/1950 Breadner et al. 313/493 2,847,603 8/1958 Engelbart 313/188 3,296,480 l/1967 Walz 313/204 3,409,792 11/1968 Martyny et a1. 313/487 3,504,217 3/1970 Roux et a1. 313/220 X 3,611,009 10/1971 McNeil ..313/204X FOREIGN PATENTS OR APPLICATIONS 949,360 9/1956 Germany 313/204 906,947 6/1945 France 313/204 906,245 3/1954 Germany 313/220 Primary ExaminerPa1mer C. Demeo Attorney, Agent, or Firm,Jerome C. Squillaro; Joseph T. Cohen [57] ABSTRACT An improved electric discharge lamp, such as a fluorescent lamp, is described in accord with one embodiment of the invention as comprising a tapered cylindrical envelope having a helically-shaped channel of nonuniform pitch therein for providing a discharge path circumferentially around the envelope with a pair of electrodes disposed adjacent each end of the discharge path. Means are also disclosed for coating the interior surface of the envelope with a luminescent material and filling the envelope with an ionizable gas.

1 Claim, 4 Drawing Figures PATENTEU AUG 1 2197s STARTER LAMP BALLAST A.C. SOURCE TAPERED HELICAL COMPACT FLUORESCENT LAMP The present invention relates to electric discharge lamps having ionizable gas discharge paths with luminescent material coated on the discharge path.

Researchers have been attempting over the years to develop compact electric discharge lamps, such as fluorescent lamps, as screw-in replacements for the standard incandescent lamps. This development, unfortunately, has been hampered by the inability to devise a suitable structural arrangement for the lamp which is amenable to high speed mass production at a reasonable cost. Further, the inability to provide uniform coatings of luminescent materials to unusual shaped lamps with little damage to the luminescent coating has proved to be a serious problem.

Attempts to solve the aforementioned problems and provide a helical fluorescent lamp are described in U.S. Pat. Nos. 2,491,847 and 2,501,375 to Breadner et al. For example, U.S. Pat. No. 2,501,375 appears to disclose a helical fluorescent lamp including two molded cylinders in which an electric discharge passage is formed by a helical groove in one or both cylinders. One of the major difficulties encountered in this structure is the requirement that the two glass cylinders be sealed together all along the ridge between adjacent turns of the groove, in order to avoid short-circuit paths for the discharge. This seal is difficult to implement in mass production, the thermal stresses are very likely to crack such a complicated sharp-angle joint.

U.S. Pat. No. 2,491,847 also employs two mating, cylindrical glass parts, one of which has a helical groove to provide the arc path. Here a short-circuit of the discharge is prevented by a close fit between the inner and outer glass parts along the ridge between adjacent turns of the groove. This approach, however, requires impractically close tolerances for glass-working machinery, as is explained further below, and has not been commercially acceptable.

It is therefore a general object of this invention to provide a compact fluorescent lamp that can be easily produced with high speed machinery at reasonable cost.

It is a further object of this invention to provide a compact fluorescent lamp that can be easily assembled without damage to luminescent coatings and does'not require impractically close tolerances.

In accord with the present invention, these and other objects are provided by a compact fluorescent lamp including two tapered cylindrically-shaped glass members in nested coaxial relationship, one or both of which are grooved to form the discharge path. The two glass members are sealed together at the ends thereof, with an electrode disposed adjacent each end of the discharge path and supported by at least one of the cy lindrical members.

The cylindrical members are formed, for example, by blowing glass into molds that are split so as to release the blown member. This method allows satisfactory control of the outside dimensions of the blown glass members. However, due to the viscous nature of glass it is very difficult to hold the glass thickness, i.e., the inside dimension of the members, to a value that is the same for each piece in a large production run. Furthermore, the glass members must be annealed after forming, and in annealing they will shrink by an amount that is difficult to keep constant. By providing the cylindrical members with a taper, the present invention makes possible a close match between the members despite the variable dimensions, since such variations are auto matically compensated for by the tapered fit.

The novel features of my invention are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a compact helicallyshaped fluorescent lamp in accord with one embodiment of my invention characterized by a helicallyshaped discharge path of nonuniform pitch;

FIG. 2 is a vertical cross-sectional view of FIG. 1;

FIG. 3 is a plan view of an evacuable envelope for a compact helically-shaped fluorescent lamp in accord with the same embodiment of my invention; and

FIG. 4 is an electrical schematic diagram of one configuration for operating a fluorescent lamp in accord with my invention.

FIG. 1 illustrates an improved helically-shaped fluorescent lamp 10 characterized by a tapered, cylindrical shape with a helically-shaped discharge path formed circumferentially around the tapered cylindrical body of the lamp. A standard screw-in base 11 supports a suitable ballast device 21 located within the central re gion of the lamp for controlling the discharge current through the lamp. The ballast device 21 supports the lamp 10 by suitable means illustrated for convenience by flanges 23 and 24.

FIG. 2, a vertical cross-sectional view of FIG. 1, illustrates in greater detail the construction of the fluorescent lamp 10 in accord with my invention. More specifically, FIG. 2 illustrates the lamp 10 as comprising an inner glass member 112 of tapered cylindrical shape. The inner glass member 12 includes a pair of electrodes 13 and 14 adjacent the ends thereof and within the helically-shaped discharge path 15 formed by a groove in an outer glass member 16, also of tapered cylindrical shape similar to that of the inner glass member 12 so that the inner and outer glass members 12 and 16 nest together in coaxial relationship with each other.

The inner and outer glass members 12 and 16, respectively, are constructed of suitably blown glasses, such as soda lime or pyrex, for example. Electrodes 13 and 14 may, for example, comprise tungsten filaments coated with suitable activating materials to initiate and maintain the desired gaseous discharge within the helically-shaped discharge path 15.

One of the novel features of the helically-shaped fluorescent lamp constructed in accord with my invention is the asymmetric shape of the discharge path or channel 15. More specifically, the fabrication of lamps in accord with my invention contemplates the use of split molds, such as those utilized in the fabrication of standard incandescent lamps. However, unlike the standard incandescent lamp which has a smooth contoured surface which permits easy release of the glass envelope from a mold, cylindrically-shaped glass members with a symmetrical helical channel formed therein do not uniform pitch is unacceptable for high-speed machinery necessary for mass production.

In accord with one embodiment of my invention, however, the foregoing problem is overcome by providing a helix which is characterized by a nonuniform pitch around the circumference of the tapered cylindrical members 12 and 16. More specifically, the outer, grooved member 16 is made, for example, by blowing glass into a two-piece mold that is designed so that the helix angle or pitch is substantially zero where the helix crosses the plane where the two mold halves join, i.e., at the mold parting plane 17 illustrated in FIG. 3. Therefore, the mold and blown glass surfaces are perpendicular to the mold parting plane 17 where they cross it. By constructing the mold for the outer glass member 16 in this manner, the member 16 is easily released from the mold. For a more detailed description of the mold construction, reference may be made to concurrently-filed application Ser. No. 465,904, filed May 1, 1974, of common assignee as the instant application, the entire disclosure of which is incorporated herein by reference thereto. 7

In the embodiment of my invention shown in FIGS. 1 to 3, the inner glass member 12 does not contain a spiral groove. In accord with alternative embodiments of my invention, the inner glass member 12 may also contain a spiral groove so as to produce an arc path of approximately circular cross-section, or only the inner member 12 may be grooved so as to produce an arc path of approximately semicircular cross-section so that the lamp surface is flat on the outer periphery. In these alternative embodiments, the inner glass member 12 is made in a two-piece mold that is designed so that the helix angle or pitch is substantially zero where the helix cross the plane where the two mold halves join.

Yet another feature of my invention which makes it particularly conducive to high-speed mass production is the manner in which luminescent materials, such as phosphors, are applied uniformly to the inner and outer glass members 12 and 16. Specifically, the luminescent material is applied to the outer surface of the inner member 12 and the inner surface of the outer member 16 prior to nesting them coaxially together. For best lamp efficacy, the outer surface of the inner member 12 is coated with a thicker layer of luminescent material than that applied to the inner surface of the outer member 16 so that the thick layer of luminescent material acts as a reflector, thereby preventing light loss into the interior of the lamp. Alternatively, a layer of re- 7 flecting material may be applied beneath the coating of luminescent material on the outer surface of the inner member 12. After coating the inner and outer glass members 12 and 16 with the desired luminescent material, the members are slid together and nested coaxially as illustrated in FIG. 2. The ends 18 and 19 of the lamp are then sealed together, for example by heating the glass material to its softening temperature to provide an evacuable envelope. The envelope is then evacuated through a tubulation 25 and filled with an ionizable filling including mercury and an inert starting gas such as argon at a pressure of a few Torr. As in standard fluorescent lamps, the electric discharge occurring along the discharge path causes the generation of ultraviolet radiation which excites the luminescent coating applied to the inner surfaces of the lamp and thus produces visible light.

FIG. 4 illustrates a typical electrical schematic diagram of the manner in which the lamp may be operated. Specifically, FIG. 4 illustrates a source of alternating current voltage applied to a ballast 21 which controls the current through the fluorescent lamp 10. A starter 22 is serially connected with the lamp filaments and the ballast to provide suitable ignition of the discharge upon application of the alternating current.

In accord with still another feature of my invention, the ballast 21 and starter 22 may be conveniently located within the central portion of the lamp 10 as illustrated in FIG. 1. The ballast and starter are supported by a screw thread 1 1 and they in turn support the lamp 10 by suitable means illustrated for convenience by flanges 23 and 24. Those skilled in the art can readily appreciate that other techniques for assemblying the lamp with a ballast and starter, if required or desired, may be employed and the aforementioned description is merely illustrative of one such technique.

From the foregoing description, those skilled in the art can readily appreciate that my invention overcomes numerous problems of prior art fluorescent lamps of helical construction and provides a compact fluorescent lamp that is easily produced by high-speed machinery at reasonable cost.

It should be understood that the foregoing description and embodiments of my invention are intended by way of example only. Obviously many modifications are possible. For example, whereas the outer glass member is illustrated as having a helically-shaped channel of nonuniform pitch for providing a discharge path winding circumferentially around the lamp envelope, other also are alsos acceptable. For example, the discharge path may comprise a serpentine-shaped groove having a vertical orientation relative to the axis of the envelope. Still other configurations are possible and obvious to those skilled in the art in view of the above teachings. Still further, other techniques for starting and controlling the discharge may be employed if desired. Accordingly, the appended claims are intended to cover all such modifications as fall within the true spirit and scope of this invention.

What I claim as new and desire to secure by Patent of the United States is:

1. An electric discharge lamp comprising:

an evacuable envelope including inner and outer glass members of tapered cylindrical shape in nested coaxial relationship, at least one of said members having a helically-shaped channel therein for providing an electrical discharge path; said channel characterized by a non-uniform pitch around the circumference of said cylindrical member wherein the helix angle of said channel is a minimum where the channel crosses a vertical plane passing through said envelope and is a maximum at to said plane, thereby providing an asymmetric helically-shaped channel;

a pair of electrodes, one disposed adjacent each end of said channel and supported by at least one of said glass members;

a luminescent material covering the interior walls of said glass members at least along said discharge path, the luminescent material covering the interior wall of said inner glass member being thicker than the luminescent material covering the interior wall of said outer glass member;

Letters electric current to said ballast means; means sealing together the ends of said inner and outer glass members; and

a gaseous filling in said discharge path. 

1. An electric discharge lamp comprising: an evacuable envelope including inner and outer glass members of tapered cylindrical shape in nested coaxial relationship, at least one of said members having a helically-shaped channel therein for providing an electrical discharge path; said channel characterized by a non-uniform pitch around the circumference of said cylindrical member wherein the helix angle of said channel is a minimum where the channel crosses a vertical plane passing through said envelope and is a maximum at 90* to said plane, thereby providing an asymmetric helically-shaped channel; a pair of electrodes, one disposed adjacent each end of said channel and supported by at least one of said glass members; a luminescent material covering the interior walls of said glass members at least along said discharge path, the luminescent material covering the interior wall of said inner glass member being thicker than the luminescent material covering the interior wall of said outer glass member; ballast means electrically connected to said electrodes for regulating electric current flow along said discharge path, said ballast means positioned within the opening defined by said inner glass member; means including a screw-in base for providing said electric current to said ballast means; means sealing together the ends of said inner and outer glass members; and a gaseous filling in said discharge path. 